[FSDP][Easy] `zeros` -> `empty` for immediately freed tensors (#106857)
Since we immediately free these tensors' storage (via `_free_storage()`), there is no reason to zero them after allocation:
https://github.com/pytorch/pytorch/blob/92e5b124c8feae01450ba020ed95a5ce8a327fa8/torch/distributed/fsdp/flat_param.py#L1140-L1145
https://github.com/pytorch/pytorch/blob/92e5b124c8feae01450ba020ed95a5ce8a327fa8/torch/distributed/fsdp/flat_param.py#L1155-L1161
https://github.com/pytorch/pytorch/blob/92e5b124c8feae01450ba020ed95a5ce8a327fa8/torch/distributed/fsdp/flat_param.py#L1166-L1171
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106857
Approved by: https://github.com/Skylion007
